Figure 2.

Effect of ArcZ overexpression on acid resistance of E. coli cells. (A) Survival rates of MG1655 transformed with IPTG-inducible RNA expression plasmid overexpressing ArcZ. Exponentially growing Escherichia coli cells were exposed to pH 2.0 for 1 h. Expression of ArcZ was increased with increasing IPTG concentrations. The RNA expression vector, pHMB1, was used as the control plasmid. Before and after acid exposure, cells were serially diluted in LB media and plated on LB agar plates. The survival rate was calculated based on the ratio of CFU of cells after acid exposure to CFU before acid exposure. Tenfold serial dilutions of cultures exposed to acid challenge were additionally spotted on LB agar and grown overnight. Cells containing the vector plasmid grown in the presence of 1 mmol/L were used as a control, instead of cells containing RNA expression plasmids grown at zero concentrations of IPTG. (B) IPTG-induced overexpression of ArcZ was analyzed by Northern blot analysis. A ³²P-labeled antisense oligonucleotide for ArcZ was used as the probe.